A primary application of condensate water polishing systems is in the large capacity heat power unit (more than 300MW) in a heat power plant. When condensate water passes through a mixed bed containing the cation and anion exchange resins, the ionic impurities in the condensate water are removed by ionic exchange with these resins, thus the condensate water is purified. Meantime, the cation and anion exchange resins will be exhausted after being used for a certain period. At that time, these exhausted resins must be regenerated to restore their capacity to remove the ionic impurities from water in order to be reused. However, said regeneration treatment needs to be done outside the condensate water polishing systems, which is called “external regeneration”, since the power plant must be operated continuously. Therefore, during the regeneration treatment, the exhausted anion and cation resins contained in the mixed bed must be separated, and after this, the separated anion and cation resins are regenerated respectively. The higher the separation degree is, the better effect the resin regeneration reaches, thereby the better effect the recycle resins can realize. Such separation of the cation and anion resins is conventionally accomplished by passing water upwardly through a filter provided at the bottom of a separation and regeneration vessel. Said mixed resins are put on the filter, and they are separated by difference in specific gravity. The less dense resin floats upwardly, and the more dense resin goes down.
The structure of conventional filter is a perforated board type water filter comprising a board with a plurality of holes and a plurality of sub-filters mounted on the respective holes correspondingly. Such a structure has dead zones around the sub-filters, and this will result in an uneven filtration and create some dead zones of transporting the resins. Another structure of conventional filter is a porous water distributor which is made by adhering quartz sands with epode resin. Such a structure is too thick and prone to be blocked, and the quartz sands on the surface are liable to drop and contaminate the cation and anion resins. Another structure of conventional filter is disclosed in Chinese utility model patent, Publication No. CN2350122Y, Patent No. ZL98224787.7,published on Nov. 24, 1999, entitled “a water distributer used for separation of anion and cation exchange resins used in polishing condensate water”. This patent discloses a filter made from a microporous net board which is formed by sintering stainless steel wires. This patent has significant improvement in term of techniques and effect. Such microporous net board has the following advantages: it can evenly distribute the water, the paths of said micropores are relatively straight and can't be blocked easily, and the cation and anion resins can be well stratified by the water while will not create dead zones. However, the structure of said patent also has following disadvantages: it lacks sufficient firmness and can be deformed easily. Its acid resistance and oxidation resistance properties are both poor.
Accordingly, in order to overcome the above problems, this invention provides a frustum filter or truncated cone filter used for separation of cation and anion exchange resins, which is used in condensate water polishing system or apparatus and enable the cation and anion exchange resins to smoothly flow on the frustum filter. This frustum filter has novel structure and can realize even filtration.